the problem you will have is three fold
1. The roush in those years I believe have a normal mustang VIN so to a bank its just aGT nothing special
2. Its older so the loan rates will be bad or not possible for your car which will have a higher value so anyone purchasing will just about have to have cash or have something you want to trade for
3. The mods dont really translate into dollar for dollar and you have to find someone that wants the mods
but I am sure the market is there if you have the time to wait.